Low-frequency excitation and high-frequency impact coupled void lining test device and method

Abstract

The invention provides a low-frequency excitation and high-frequency impact coupled void lining test device and method, and belongs to the technical field of tunnel instability monitoring, and the device comprises a lining loading system, a low-frequency excitation system and a high-frequency impact system. The loading mechanism simulates the surrounding rock load borne by the lining in the circumferential direction, and the surrounding rock load borne by the lining can be simulated by adjusting parameters such as the magnitude and the direction of loading force. The vibration exciter is matched with the power amplifier, low-frequency and high-amplitude vibration matched with the axle load characteristics of the train can be generated, and the fatigue damage effect on the lining caused by long-term running of the train is simulated. When the electric detacher controls the drop hammer to be separated from the truss and fall freely, high-frequency transient impact force can be generated, and the transient load effect of a lining impacted by falling rocks is simulated. According to the test device, through multi-physics field coupling loading, the problems that a void lining damage mechanism is unclear and prediction means are deficient are solved, a complete technical chain is provided for railway tunnel structure safety, and the test device has academic value and engineering popularization significance.

Description

Technical Field

[0001] The present invention belongs to the technical field of tunnel instability monitoring. More specifically, it relates to a test device and method for an air-gap lining coupling low-frequency excitation and high-frequency impact. Background Art

[0002] Due to the early construction of some railways in China and the limitations of technical conditions at that time, the shrinkage of 200# concrete was large and the construction technology was insufficient, resulting in insufficient compactness of the contact surface with the surrounding rock after pouring, and finally forming an air-gap disease. The air-gap lining of railway tunnels has long been subjected to the excitation of low-frequency and high-amplitude loads of large axle loads and long formation trains and the high-frequency impact of falling rocks. The structural performance of the lining deteriorates, leading to the possibility of cracking at the air-gap part of the lining and further causing falling. The sudden falling of the lining will not only cause local collapse of the tunnel and reduce the overall structural stability, but also may cause the running train to derail and threaten the lives and health of personnel.

[0003] The process of lining cracking is progressive. After multiple stress actions, environmental changes or the accumulation of other external loads, until a critical point is reached at a certain moment, resulting in sudden falling of the lining structure. When there is an air-gap disease behind the lining, under the combined action of train low-frequency excitation, surrounding rock pressure and falling rock high-frequency impact, the originally tiny cracks or loose parts may rapidly expand, resulting in a serious sudden falling phenomenon of the lining, and the falling time and damage degree are difficult to predict. Summary of the Invention

[0004] The purpose of the present invention is to provide a test device for an air-gap lining coupling low-frequency excitation and high-frequency impact, so as to simulate the combined action of train low-frequency excitation, surrounding rock pressure and falling rock high-frequency impact, and achieve the purpose of predicting the response characteristics of the lining.

[0005] To achieve the above object, the technical solution adopted by the present invention is: to provide a test device for an air-gap lining coupling low-frequency excitation and high-frequency impact, including: A lining loading system, including a main frame body, a lining ring and a loading mechanism. The lining ring and the loading mechanism are both arranged inside the main frame body. The loading mechanism is arranged circumferentially on the lining ring and is used to simulate the surrounding rock load in the circumferential direction of the lining; A low-frequency excitation system, including a support beam, an exciter and a power amplifier. The support beam axially penetrates the lining ring. The exciter is connected to the support beam. The power amplifier is electrically connected to the exciter and is used to simulate the low-frequency excitation of the train passing through the lining; A high-frequency impact system, comprising a top frame body, a truss, an electric hook release, and a drop hammer. The top frame body is fixed to the top of the main frame body. The truss is arranged on the top of the top frame body through the electric hook release. The drop hammer is arranged at the bottom of the truss and directly above the lining ring. The drop hammer detaches from the truss to impact the lining ring, for simulating the high-frequency impact of falling stones on the lining.

[0006] In a possible implementation, it further includes a monitoring system, and the monitoring system includes: A plurality of three-axis accelerometers, respectively arranged circumferentially on the inner wall of the lining ring. The three-axis accelerometers are used to detect vibration signals in three directions of the lining ring; A vibration analyzer, electrically connected to the plurality of three-axis accelerometers, for converting the vibration signals into time-frequency domain signals to simulate the main frequency and main eigenvalue of the lining ring.

[0007] In a possible implementation, a plurality of jacks are sequentially arranged along the length direction at the bottom of the main frame body, and the lining ring is arranged on the plurality of jacks.

[0008] In a possible implementation, the loading mechanism includes: A plurality of servo electric cylinders, arranged circumferentially on the lining ring. The outer ends of the servo electric cylinders are fixed to the main frame body, and a rigid plate body is fixed to the inner ends of the servo electric cylinders. A nylon gasket that presses against the outer wall of the lining ring is arranged on the inner side surface of the rigid plate body, and the inner side surface of the nylon gasket has a conforming surface adapted to the outer wall of the lining ring.

[0009] In a possible implementation, the vibrator is suspended at the lower end of the support beam through an elastic member. The vibrator is located inside the lining ring and within the longitudinal projection area of the lining ring.

[0010] In a possible implementation, sliding rods are longitudinally arranged on both sides of the top frame body, and sliding sleeves are respectively arranged on both sides of the truss. The sliding sleeves are slidably matched with the sliding rods on the same side, and the electric hook release is used to drive the truss to lift.

[0011] The beneficial effects of the experimental device for debonded lining with low-frequency excitation and high-frequency impact coupling provided by the present invention are as follows: Compared with the prior art, a lining ring and a loading mechanism are provided inside the main frame of the lining loading system. The loading mechanism is arranged circumferentially around the lining ring and can simulate the surrounding rock load borne by the lining circumferentially. By adjusting parameters such as the magnitude and direction of the loading force, the surrounding rock load borne by the lining can be simulated. In the low-frequency excitation system, the support beam axially penetrates the lining ring, and the vibrator is connected to the support beam. Cooperating with the power amplifier, it can generate low-frequency high-amplitude vibrations matching the characteristics of the train axle load, simulating the fatigue damage effect on the lining caused by the long-term operation of the train. In the high-frequency impact system, the top frame is fixed on the top of the main frame, the truss is arranged on the top of the top frame through an electric unhooking device, and the drop hammer is located at the bottom of the truss and directly above the lining ring. When the electric unhooking device controls the drop hammer to break away from the truss and freely fall, a high-frequency transient impact force can be generated, simulating the instantaneous load effect of a falling rock hitting the lining. These three systems cooperate with each other to achieve the multi-physical field coupling of "static loading of surrounding rock pressure + low-frequency excitation of the train + high-frequency impact of falling rocks", highly restoring the complex stress environment faced by the lining during actual operation.

[0012] Through the collaborative work of multiple systems, this experimental device can highly restore the actual complex stress environment of the lining. The lining loading system simulates the surrounding rock pressure, the low-frequency excitation system generates the low-frequency excitation of the train, and the high-frequency impact system simulates the high-frequency impact of falling rocks. The three cooperate to achieve the multi-physical field coupling of "static loading of surrounding rock pressure + low-frequency excitation of the train + high-frequency impact of falling rocks", breaking through the limitations of traditional tests, realizing the collaborative loading of low-frequency and high-frequency loads, filling the research gap of the coupling effect, quantitatively analyzing the time-sequence coupling effect of the loads, reducing the operation safety risk, and revealing the probability distribution law of lining spalling. Through the multi-physical field coupling loading, this experimental device solves the problems of unclear failure mechanism and lack of prediction means for debonded linings, provides a complete technical chain for the structural safety of railway tunnels, and has both academic value and engineering promotion significance.

[0013] The present invention also provides a test method for debonded lining with low-frequency excitation and high-frequency impact coupling, which uses the experimental device for debonded lining with low-frequency excitation and high-frequency impact coupling, and includes the following steps: S1. Fabricate a steel mold in proportion, use the steel mold to pour the lining ring and install it in the main frame; S2. Install a loading mechanism in the main frame, and the loading mechanism tightly presses the lining ring circumferentially to simulate the surrounding rock load of the lining circumferentially; S3. Install a vibrator on the support beam, the support beam axially penetrates the lining ring and makes the vibrator located inside the lining ring, and electrically connect the vibrator to a power amplifier; S4: Install the truss on the electric unhooking device at the top of the top frame, and install a drop hammer at the bottom of the truss; S5: Turn on the vibrator to simulate the low-frequency excitation of the train passing through the lining, and disconnect the electric decoupler so that the drop hammer breaks away from the truss by inertia to impact the lining ring to simulate the high-frequency impact of the falling rock on the lining. S6: Obtain the single-factor data of the low-frequency excitation or high-frequency impact, or obtain the coupled data of the low-frequency excitation and high-frequency impact.

[0014] In a possible implementation manner, in step S1, a 1:10 steel mold is made through on-site measurement or actual drawings. According to the reduced-scale model test, the elastic modulus is taken as 1 / 10 of the prototype concrete. After pouring the lining ring, it is cured indoors for 28 days to reach the standard compressive strength, and then the steel mold is removed.

[0015] In a possible implementation manner, in step S3, the power amplifier is connected to the digital signal source, and the digital signal source is connected to the computer control device, and the output mode is two-channel synchronous output.

[0016] In a possible implementation manner, in step S4, the electric decoupler controls the lifting adjustment of the truss in the top frame body, and different masses of drop hammers are replaced to simulate the erosion of the lining ring by different magnitudes of impact forces.

[0017] The beneficial effect of the test method for the voided lining with coupled low-frequency excitation and high-frequency impact provided by the present invention is as follows: Compared with the prior art, the test method for the voided lining with coupled low-frequency excitation and high-frequency impact uses the above test device, so it has the same beneficial effects as the above test device, which will not be elaborated here. Description of the Drawings

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0019] Figure 1 It is a schematic structural diagram of the test device for the voided lining with coupled low-frequency excitation and high-frequency impact provided by the embodiments of the present invention; Figure 2 For Figure 1 The partial enlarged view at M in

[0020] In the figure: 1, main frame body; 2, lining ring; 3, servo electric cylinder; 4, rigid plate body; 5, nylon gasket; 6, support beam; 7, vibrator; 8, power amplifier; 9, top frame body; 10, truss; 11, electric decoupler; 12, drop hammer; 13, sliding rod; 14, sliding sleeve; 15, power supply; 16, three-axis accelerometer; 17, vibration analyzer; 18, jack. Detailed implementation manners

[0021] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0022] Unless otherwise clearly defined, when using terms such as "first", "second" or "third", etc., they are all used to distinguish different objects and are not used to describe a specific order.

[0023] Unless otherwise clearly defined, for orientation terms, when using terms such as "center", "lateral", "longitudinal", "horizontal", "vertical", "top", "bottom", "inner", "outer", "upper", "lower", "front", "rear", "left", "right", "clockwise", "counterclockwise", "high", "low", etc. to indicate the orientation or position relationship, it is based on the orientation and position relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, so it cannot be understood as limiting the specific protection scope of the present invention.

[0024] Please refer to Figure 1 , and now the test device for the debonded lining with low-frequency excitation and high-frequency impact provided by the present invention will be described. The test device for the debonded lining with low-frequency excitation and high-frequency impact includes a lining loading system, a low-frequency excitation system and a high-frequency impact system. The lining loading system includes a main frame body 1, a lining ring 2 and a loading mechanism. The lining ring 2 and the loading mechanism are both arranged inside the main frame body 1. The loading mechanism is arranged in the circumferential direction of the lining ring 2 and is used to simulate the surrounding rock load in the circumferential direction of the lining. The low-frequency excitation system includes a support beam 6, a vibrator 7 and a power amplifier 8. The support beam 6 axially penetrates the lining ring 2. The vibrator 7 is connected to the support beam 6. The power amplifier 8 is electrically connected to the vibrator 7 and is used to simulate the low-frequency excitation of the train passing through the lining. The high-frequency impact system includes a top frame body 9, a truss 10, an electric unhooking device 11 and a drop hammer 12. The top frame body 9 is fixed on the top of the main frame body 1. The truss 10 is arranged on the top of the top frame body 9 through the electric unhooking device 11. The drop hammer 12 is arranged at the bottom of the truss 10 and is located directly above the lining ring 2. The drop hammer 12 detaches from the truss 10 to impact the lining ring 2 and is used to simulate the high-frequency impact of falling rocks on the lining.

[0025] The experimental device for an air void lining coupling low-frequency excitation and high-frequency impact provided by the present invention, compared with the prior art, has a lining ring 2 and a loading mechanism arranged inside the main frame body 1 of the lining loading system. The loading mechanism is arranged circumferentially around the lining ring 2 and can simulate the surrounding rock load borne by the lining circumferentially. By adjusting parameters such as the magnitude and direction of the loading force, the surrounding rock load borne by the lining can be simulated. In the low-frequency excitation system, the support beam 6 axially penetrates the lining ring 2, and the vibrator 7 is connected to the support beam 6. Cooperating with the power amplifier 8, it can generate low-frequency high-amplitude vibrations matching the characteristics of the train axle load, simulating the fatigue damage effect on the lining caused by the long-term operation of the train. In the high-frequency impact system, the top frame body 9 is fixed to the top of the main frame body 1, the truss 10 is arranged on the top of the top frame body 9 through the electric unhooking device 11, and the drop hammer 12 is located at the bottom of the truss 10 and directly above the lining ring 2. When the electric unhooking device 11 controls the drop hammer 12 to break away from the truss 10 and freely fall, a high-frequency transient impact force can be generated, simulating the instantaneous load effect of a falling rock hitting the lining. These three systems cooperate with each other to achieve the multi-physical field coupling of "static loading of surrounding rock pressure + low-frequency excitation of the train + high-frequency impact of falling rocks", highly restoring the complex stress environment faced by the lining during actual operation.

[0026] Through the collaborative work of multiple systems, this experimental device can highly restore the actual complex stress environment of the lining. The lining loading system simulates the surrounding rock pressure, the low-frequency excitation system generates the low-frequency excitation of the train, and the high-frequency impact system simulates the high-frequency impact of falling rocks. The three cooperate to achieve the multi-physical field coupling of "static loading of surrounding rock pressure + low-frequency excitation of the train + high-frequency impact of falling rocks", breaking through the limitations of traditional tests, realizing the collaborative loading of low-frequency and high-frequency loads, filling the research gap of the coupling effect, quantitatively analyzing the time-sequence coupling effect of the loads, reducing the operation safety risk, and revealing the probability distribution law of lining spalling. Through the multi-physical field coupling loading, this experimental device solves the problems of unclear failure mechanism and lack of prediction means for air void linings, provides a complete technical chain for the structural safety of railway tunnels, and has both academic value and engineering promotion significance.

[0027] Please refer to Figure 1The test device also includes a monitoring system, which includes a plurality of three-axis accelerometers 16 and a vibration analyzer 17. A plurality of three-axis accelerometers 16 are arranged circumferentially along the inner wall of the lining ring 2. The plurality of three-axis accelerometers 16 are connected in series in sequence and electrically connected to a power supply 15, which is fixed to the bottom of the inner wall of the lining ring 2. The vibration signals of the lining ring 2 in the horizontal, longitudinal and vertical directions can be detected synchronously. The vibration analyzer 17 is electrically connected to the accelerometer. After receiving the signal, it is converted into a time-frequency domain signal using Fourier transform, and the vibration energy distribution of different frequency components is separated, so as to obtain the main frequency and main characteristic value of the lining ring 2, and at the same time, a multi-dimensional database is constructed by combining the pressure value of the loading system and the output parameters of the exciter 7. The circumferentially distributed three-axis accelerometers 16 can cover the areas with high incidence of air escape, accurately capture the vibration characteristics of the entire space, and avoid the limitations of single-point monitoring and the omission of one-way monitoring information. The time-frequency domain signal separation technology of the vibration analyzer 17 can quantitatively analyze the multi-physical field coupling response, and can determine the degree of structural stability degradation by comparing with the complete lining benchmark data; real-time tracking of changes in parameters such as main frequency and damping ratio can warn of crack propagation, and identify signal mutations at the moment of block falling to trigger an alarm; monitoring data can also verify numerical models, correct parameters, and migrate the correspondence between vibration characteristics and disease severity established indoors to on-site monitoring, thereby realizing remote real-time monitoring of the risk of block falling of hollow linings, reducing inspection costs and improving warning efficiency.

[0028] Among them, the core function of Fourier transform is to decompose the time domain signal into the superposition of different frequency components. Its mathematical expression is: ; f ( t ) is the time domain signal, F ( ω ) is a frequency domain signal. For the actual vibration signal, the three-axis accelerometer 16 collects the vibration displacement, velocity or acceleration data of the lining ring 2 in the time dimension (time domain signal), and the Fourier transform can convert it into energy distribution in the frequency dimension (frequency domain signal).

[0029] The three-axis accelerometer 16 monitors the vibration signals of the lining ring 2 in the horizontal, longitudinal and vertical directions in real time, and generates a time domain waveform (such as a displacement-time curve). The vibration analyzer 17 first performs pre-processing such as filtering and denoising on the original signal to eliminate environmental interference and high-frequency noise to ensure signal accuracy.

[0030] The vibration analyzer 17 performs mathematical transformation on the time domain signal by discrete Fourier transform or fast Fourier transform FFT algorithm: Time domain characteristics: reflect the changes of the instantaneous amplitude and waveform period of the vibration of lining ring 2 over time, such as the instantaneous response to low-frequency excitation of trains or rockfall impact.

[0031] Frequency domain characteristics: Decompose the time-domain signal into sine / cosine components of different frequencies. Each frequency component corresponds to a specific amplitude and phase, thereby obtaining the frequency distribution of the signal (such as the main frequency and secondary frequency) and the energy proportion.

[0032] Strictly speaking, the Fourier transform directly generates a frequency-domain signal. However, the vibration analyzer 17 can achieve the comprehensive display of the "time-frequency domain signal" in the following way. By combining the short-time Fourier transform (STFT) or wavelet transform, a time dimension is introduced on the basis of frequency-domain analysis to generate a time-frequency diagram (such as the change of the frequency spectrum over time), thereby reflecting both the frequency characteristics and time distribution of the signal simultaneously. Extract the main frequency (the frequency with the highest energy proportion) and main eigenvalues (such as damping ratio and resonance frequency) from the frequency-domain signal, and associate the occurrence time in the time domain to form multi-dimensional data of "time-frequency-energy". Using the Fourier transform to convert it into a time-frequency domain signal is essentially to obtain the frequency-domain characteristics through the Fourier transform and realize the time-frequency coupling expression of the signal by combining time series analysis, that is, to obtain the "time-frequency domain signal" mentioned above.

[0033] Please refer to Figure 1 , a plurality of jacks 18 are sequentially arranged along the length direction at the bottom of the main frame body 1. The lining ring 2 is arranged on the plurality of jacks 18 to realize the support positioning of the lining ring 2 and the simulation of boundary conditions. The lining ring 2 is placed on the plurality of jacks 18. By adjusting the height of the jacks 18, the levelness and installation position of the lining ring 2 can be accurately adjusted to ensure that its axis is coaxially aligned with the support beam 6 of the low-frequency excitation system and the impact point of the drop hammer 12 of the high-frequency impact system. The jacks 18 adopt a screw or hydraulic drive method and can provide a stable vertical support force to simulate the contact state between the tunnel lining and the surrounding rock of the foundation in actual engineering. Similarly, a rigid plate body 4 and a nylon gasket 5 are sequentially arranged at the upper end of the jacks 18, so that the pressure of the jacks 18 acts on the nylon gasket 5 through the rigid plate body 4 and then evenly acts on the bottom of the lining ring 2. The installation error of the lining ring 2 can be eliminated through the fine-tuning function of the jacks 18 to avoid uneven load transfer and ensure the reliability of test data. The influence of different foundation surrounding rock conditions on the vibration response of the lining ring 2 can be simulated by adjusting the support stiffness, such as simulating the scenarios of foundation void or weak surrounding rock. By controlling the lifting amplitude of the jacks 18 at different positions, the uneven force along the longitudinal direction of the lining ring 2 can be simulated to construct an asymmetric support boundary condition and expand the simulation ability for complex engineering scenarios. The rigid support of the jacks 18 can stabilize the lining ring 2, prevent it from displacing or overturning due to vibration or impact, and at the same time facilitate the rapid installation and disassembly of the lining ring 2, improving the test efficiency. In short, the jacks 18 ensure the installation accuracy and test safety through precise adjustment and stable support, enhance the device's ability to reproduce the complex stress environment of actual tunnels, and provide key support for studying the dynamic response of void linings under different foundation constraints.

[0034] The main frame 1 includes two longitudinal beams, a bottom cross beam, a top cross beam and two diagonal braces. The two longitudinal beams are symmetrically arranged left and right; the bottom cross beam is horizontally installed at the bottom of the two longitudinal beams, and the lining ring 2 is arranged above the bottom cross beam; the top cross beam is horizontally installed at the top of the two longitudinal beams, and an avoidance notch is provided in the middle of the top cross beam. The top frame 9 is arranged at the upper end of the top cross beam and above the avoidance notch; the two diagonal braces are respectively installed on the inner sides of the tops of the two longitudinal beams and are obliquely connected to the lower end face of the top cross beam. Through the symmetrical rigid frame design, this structure uses the bottom cross beam to bear the lining ring 2 and the jack 18 system. The top cross beam integrates the high-frequency impact system and ensures the smooth impact path of the drop hammer 12 through the avoidance notch. The diagonal braces and the longitudinal beams and the top cross beam form a triangular support system, enhancing the torsional stiffness and overall stability of the top of the main frame 1, evenly distributing the vertical load and the horizontal load, suppressing the structural torsion caused by eccentric load, ensuring the accurate transfer of the load of the loading mechanism, the low-frequency excitation system and the high-frequency impact system to the lining ring 2, avoiding the interference of the deformation of the main frame 1 itself on the test results, and providing a high-strength and high-stability support system for the test device.

[0035] Please refer to Figure 1 and Figure 2, the loading mechanism includes multiple servo electric cylinders 3. The multiple servo electric cylinders 3 are arranged circumferentially on the lining ring 2. The outer ends of the servo electric cylinders 3 are fixed to the main frame 1, and a rigid plate body 4 is fixed to the inner ends of the servo electric cylinders 3. A nylon gasket 5 that presses against the outer wall of the lining ring 2 is provided on the inner side surface of the rigid plate body 4. The inner side surface of the nylon gasket 5 has a conforming surface adapted to the outer wall of the lining ring 2. During the test, the servo electric cylinder 3 drives the piston rod to axially move through the computer control system, pushing the rigid plate body 4 and the nylon gasket 5 to apply pressure to the lining ring 2 to simulate the circumferential load of the surrounding rock. The elastic compression characteristics of the nylon gasket 5 can convert the thrust into a continuously distributed surrounding rock pressure, and its compression amount has a linear relationship with the load. By real-time monitoring the cylinder displacement and output force, the magnitude and distribution pattern of the pressure can be accurately controlled. The circumferential servo electric cylinders 3 can be loaded synchronously or independently, which can not only simulate the uniform constraint of the complete surrounding rock, but also simulate the scenario of void behind the lining by reducing the local pressure, and can also adjust the pressure ratio to simulate the formation resistance coefficient of different surrounding rock grades. The conforming surface of the nylon gasket 5 fits the lining ring 2, avoiding stress concentration caused by rigid loading. Its elastic deformation can absorb vibration and ensure uniform load transfer. The servo electric cylinder 3 has high-precision displacement control and force feedback functions, can record the pressure-displacement curve in real time and calibrate the load parameters in combination with the specifications to ensure the engineering referenceability of the test conditions. In addition, by removing some servo electric cylinders 3 or reducing the loading force, a local void area can be constructed to study the stress concentration effect under the coupled load in cooperation with other systems. By replacing the gasket materials with different stiffnesses, the influence of the change in the stiffness of the surrounding rock can also be simulated. Through the mechanism of rigid drive-flexible transfer, the loading mechanism realizes the precise control and diverse simulation of the surrounding rock pressure, provides a reliable support for the study of the mechanical behavior of the void lining under the multi-physical field coupling effect, and improves the engineering applicability and scientific value of the test results.

[0036] Please refer to Figure 1, the exciter 7 is suspended at the lower end of the support beam 6 through an elastic member. The exciter 7 is located inside the lining ring 2 and within the longitudinal projection area of the lining ring 2. Two sets of elastic springs, as the moving coil suspension device, keep the exciter 7 in a suspended posture. The support beam 6 axially penetrates the lining ring 2 to form a rigid support axis, ensuring that the excitation direction is consistent with the axis of the lining ring 2. During operation, the power amplifier 8 drives the exciter 7 to generate vibrations, and the excitation force is transmitted to the lining ring 2 through the elastic springs and the support beam 6, simulating the low-frequency excitation of train loads. Among them, the elastic springs can filter high-frequency noise to ensure the purity of low-frequency signals. The amplitude of the excitation force (maximum 200 N) and the frequency (covering the train load frequency band of 0.1 - 10 Hz) can be accurately adjusted through the digital signal source and the power amplifier 8. The exciter 7 is located at the center of the longitudinal projection area of the lining ring 2, and the vibration energy is evenly transmitted radially to each point on the inner wall, avoiding stress deviation caused by eccentric excitation. It can also couple to generate a longitudinal vibration component to restore the three-dimensional vibration characteristics of the train. The elastic springs provide buffering during start-up and shutdown to prevent mechanical shock from damaging the structure. The connecting rod nuts and spring limits suppress lateral displacement to ensure stability. The built-in layout of the exciter 7 reduces the attenuation of energy transmission, making the micro-vibration monitoring system more sensitive to capture low-frequency responses. Moreover, the excitation timing can be controlled individually, facilitating the separation of the influence of multi-factor loads. This design achieves high purity, uniformity, and precise controllability of low-frequency excitation through elastic suspension and central layout, providing reliable support for the research on fatigue damage and coupling effects of voided linings.

[0037] Specifically, support legs are fixedly connected to both ends of the support beam 6, and diagonal bars are fixed between the support legs and the support beam 6 to form a rigid triangular frame structure of beam-leg-reinforcement. The support beam 6 axially penetrates the lining ring 2 and is fixed to the main frame body 1 through the support legs. The diagonal bars are made of the same material as the support beam 6 and are formed into triangular stiffeners through welding or bolt connection, which can enhance the rigidity and stability of the support system. This structure quickly transmits the vibration load generated by the exciter 7 to the main frame body 1 through the support beam 6, diagonal bars, and support legs through the triangular frame effect, shortening the force transmission path and reducing vibration energy loss. At the same time, it inhibits the bending deformation, shear slip, and lateral swing of the support beam 6 under the action of the excitation force, ensuring that the excitation direction is consistent with the axis of the lining ring 2, and improving the vibration transmission efficiency and direction accuracy. The diagonal bars can also share the stress concentration at the ends of the support beam 6, reduce the risk of fatigue cracking, extend the fatigue life of the support system, cooperate with the high-precision installation of the support legs, ensure the coaxiality of the support beam 6 and the axis of the lining ring 2, improve the consistency and repeatability of multiple groups of test data, and allow the support beam 6 to be quickly disassembled and reinstalled, shortening the test preparation time.

[0038] Please refer to Figure 1, slide bars 13 are longitudinally arranged on both sides of the top frame body 9, sliding sleeves 14 are respectively arranged on both sides of the truss 10, and the sliding sleeve 14 is slidably matched with the slide bar 13 on the same side. The electric unhooking device 11 is used to drive the truss 10 to lift and lower. In this structure, the slide bar 13 and the sliding sleeve 14 form a vertical sliding pair. The steel cable of the electric unhooking device 11 driven by the motor drives the truss 10 to move up and down along the slide bar 13, and the vertical distance between the drop hammer 12 and the crown of the lining ring 2 can be adjusted. The rigid guidance of the slide bar 13 and the sliding sleeve 14 ensures that the lateral displacement error is smaller when the truss 10 is lifted and lowered, and the impact point will not deviate too much from the crown center, ensuring the vertical transmission of the impact load. By adjusting the mass and falling height of the drop hammer 12, the impact energy gradient can be accurately controlled to simulate the impact of falling rocks of different scales; the electric unhooking device 11 supports the truss 10 to stay at any position within a specific stroke, and can simulate the fall of falling rocks at different rock layer heights.

[0039] Specifically, the electric unhooking device 11 includes a motor and a pulley block. The controller sends instructions to control the forward and reverse rotation of the motor. The motor drives the pulley block to wind and unwind the steel cable. The steel cable is connected to the top of the truss 10 and then pulls the truss 10 to lift and lower along the slide bar 13, accurately adjusting the vertical distance between the drop hammer 12 and the crown of the lining ring 2. By remote control, the risk of manual operation is avoided. It supports the computer to preset multiple groups of height parameters to achieve one-key working condition switching, improving the test efficiency. Different mass drop hammers 12 can be controlled to impact from different heights. Through automatic control and precise transmission, the electric unhooking device 11 provides a reliable height adjustment means for the high-frequency impact system, enhancing the simulation ability of the test device for impact loads in multiple scenarios.

[0040] Preferably, an installation slot is opened at the upper end of the drop hammer 12. An installation column is fixedly arranged in the middle of the lower end of the truss 10. An elastic end is arranged at the end of the installation column. The elastic end is press-fitted into the installation slot. When the truss 10 descends to the bottom after being separated from the electric unhooking device 11 and stops instantly, the drop hammer 12 continues to move downward due to inertia. At this time, a downward shearing force is generated on the elastic end by the installation slot of the drop hammer 12. When this force exceeds the friction force of the interference fit, the drop hammer 12 is separated from the elastic end and impacts the crown of the lining ring 2 in a free-fall state.

[0041] Based on the same inventive concept, the present invention also provides a test method for an air void lining with low-frequency excitation and high-frequency impact coupling, which uses the above-mentioned test device for an air void lining with low-frequency excitation and high-frequency impact coupling, and includes the following steps: S1. Make a steel mold in proportion, pour the lining ring 2 using the steel mold and install it in the main frame body 1.

[0042] Fabricate a 1:10 scaled steel mold according to on-site measurements or design drawings. Prepare a mixture of cement and gravel in a certain proportion and pour the lining ring 2 model. After 28 days of indoor curing, the lining ring 2 reaches the standard compressive strength. Remove the steel mold and install the lining ring 2 on the jack 18 at the bottom crossbeam of the main frame 1. Adjust the levelness and installation height through the jack 18 to ensure that the axis of the lining ring 2 is coaxial with the support beam 6 and the impact point of the drop hammer 12.

[0043] The scaled model combines the similarity ratio theory (parameters such as elastic modulus and load are scaled proportionally), which greatly reduces the labor and material costs of the prototype test while ensuring the test accuracy. For example, the load of the shaker 7 is reduced from 1 kN of the prototype to 200 N. The standardized mold and curing process ensure the consistency of the lining ring 2 model and improve the comparability of multiple groups of test data.

[0044] S2. Install a loading mechanism inside the main frame 1. The loading mechanism circumferentially compresses the lining ring 2 to simulate the surrounding rock load in the circumferential direction of the lining.

[0045] Install multiple servo electric cylinders 3 circumferentially on the main frame 1. The inner side tightly presses the outer wall of the lining ring 2 through a nylon gasket 5 with a conformal surface. The servo electric cylinder 3 integrates a high-precision pressure sensor, which can collect the pressure data of the object or equipment to be measured in real time. Configure complex algorithms to quickly and accurately analyze and process the massive data collected, and automatically calculate key pressure detection indicators such as pressure peak value, pressure average value, and pressure fluctuation range. Drive the servo electric cylinder 3 to move axially through the computer control system. According to the formation resistance coefficient of class Ⅲ - Ⅴ surrounding rock in the "Railway Tunnel Design Code", adjust the compression amount of the nylon gasket 5. For example, the compression amount of 0.5 - 5 mm corresponds to different surrounding rock grades to simulate the surrounding rock pressure distribution in the circumferential direction of the lining, with uniform or local voids. The tensile elastic modulus of the nylon gasket 5 is 25.5 - 27.5 MPa, and the bending elastic modulus is 2000 MPa - 3000 MPa.

[0046] The flexible nylon gasket 5 and the conformal surface design achieve uniform load transfer, avoid stress concentration caused by rigid loading, and truly restore the contact characteristics between the surrounding rock and the lining. Independently controlling the servo electric cylinder 3 can quickly construct a local void scenario, such as unloading in the 60° range of the vault, providing a basis for studying the stress concentration in the void area under the coupled load.

[0047] S3. Install a shaker 7 on the support beam 6. The support beam 6 axially penetrates the lining ring 2 and positions the shaker 7 inside the lining ring 2. Electrically connect the shaker 7 to a power amplifier 8.

[0048] Suspend the vibrator 7 at the lower end of the support beam 6 through an elastic spring, which is located at the center of the longitudinal projection area of the lining ring 2. Both ends of the support beam 6 are fixed by support legs with diagonal bars to ensure that the vibration direction of the vibrator 7 is consistent with the axis of the lining ring 2. The vibrator 7 is connected to a power amplifier 8 and a digital signal source, and signals such as sine waves and on-site train vibration waveforms can be input, with a frequency range of 0.1 - 10 Hz and an amplitude range of 0 - 200 N.

[0049] The elastic suspension system filters high-frequency noise (purity > 80 dB) to ensure the accuracy of low-frequency excitation; the central symmetric layout enables the lining ring 2 to be uniformly vibrated in the whole circumferential direction, simulating the three-dimensional vibration characteristics of train loads. The excitation frequency and amplitude can be independently adjusted to separate the fatigue damage effects of different train operation conditions (such as low-speed freight and high-speed passenger) on the lining.

[0050] S4: Install the truss 10 on the electric hook release 11 at the top of the top frame body 9, and install a drop hammer 12 at the bottom of the truss 10.

[0051] Install the truss 10 on the sliding rods 13 on both sides of the top frame body 9 through a sliding sleeve 14, and install a drop hammer 12 with a replaceable mass at the bottom. The electric hook release 11 is connected to the truss 10 by a steel cable, and the truss 10 is remotely controlled by a controller to lift and lower to the target height to ensure that the impact point of the drop hammer 12 is aligned with the crown of the lining ring 2.

[0052] The guiding system of the sliding rods 13 and the sliding sleeve 14 and the high-precision control of the electric hook release 11 ensure that the drop hammer 12 impacts vertically and the energy is controllable. The impact simulation of the drop hammer 12 reproduces the high-frequency load scenario of rockfall in an actual tunnel.

[0053] S5: Turn on the vibrator 7 to simulate the low-frequency excitation of the train passing through the lining, and disconnect the electric hook release 11 to make the drop hammer 12 break away from the truss 10 by inertia and impact the lining ring 2 to simulate the high-frequency impact of falling stones on the lining.

[0054] First, apply static surrounding rock pressure through the loading mechanism, and then start the vibrator 7 to output low-frequency signals to simulate train loads; after the low-frequency excitation is stable, the electric hook release 11 releases the steel cable to make the drop hammer 12 fall freely, realizing the multi-physical field coupling of "static surrounding rock pressure + low-frequency excitation + high-frequency impact".

[0055] The coupling loading with controllable timing can separate the action effects of different load types and reveal the critical conditions for the lining to expand from micro-cracks to sudden block shedding. Dynamically adjust the loading sequence and parameters to simulate the load accumulation effect during the long-term operation of the tunnel.

[0056] S6: Obtain single-factor data of low-frequency excitation or high-frequency impact, or obtain coupling data of low-frequency excitation and high-frequency impact.

[0057] The vibration signals of the lining ring 2 are collected in real time by the circumferentially arranged three-axis accelerometer 16. The vibration analyzer 17 converts the signals into time-frequency domain data through Fourier transform, and extracts characteristic parameters such as the main frequency, amplitude, and damping ratio. By comparing the vibration characteristics of the complete lining and the voided lining, the corresponding relationship between load-deformation-damage is established.

[0058] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An experimental device for debonded linings coupling low-frequency excitation and high-frequency impact, characterized in that, Including: A lining loading system, including a main frame (1), a lining ring (2) and a loading mechanism. The lining ring (2) and the loading mechanism are both arranged inside the main frame (1). The loading mechanism is arranged circumferentially of the lining ring (2) and is used to simulate the surrounding rock load in the circumferential direction of the lining. A low-frequency excitation system, including a support beam (6), a vibrator (7) and a power amplifier (8). The support beam (6) axially penetrates the lining ring (2). The vibrator (7) is connected to the support beam (6), and the power amplifier (8) is electrically connected to the vibrator (7) and is used to simulate the low-frequency excitation of a train passing through the lining. A high-frequency impact system, including a top frame (9), a truss (10), an electric unhooking device (11) and a drop hammer (12). The top frame (9) is fixed to the top of the main frame (1). The truss (10) is arranged on the top of the top frame (9) through the electric unhooking device (11). The drop hammer (12) is arranged at the bottom of the truss (10) and is located directly above the lining ring (2). The drop hammer (12) detaches from the truss (10) to impact the lining ring (2) and is used to simulate the high-frequency impact of falling rocks on the lining.

2. The device for testing the debonded lining with coupling of low-frequency excitation and high-frequency impact according to claim 1, characterized in that, It further includes a monitoring system, and the monitoring system includes: A plurality of three-axis accelerometers (16) are respectively arranged circumferentially on the inner wall of the lining ring (2). The three-axis accelerometers (16) are used to detect the vibration signals in three directions of the lining ring (2). A vibration analyzer (17) is electrically connected to the plurality of three-axis accelerometers (16) and is used to convert the vibration signals into time-frequency domain signals to simulate the main frequency and main characteristic values of the lining ring (2).

3. The test device for the debonded lining with coupling of low-frequency excitation and high-frequency impact according to claim 1 or 2, wherein A plurality of jacks (18) are sequentially arranged along the length direction at the bottom of the main frame (1), and the lining ring (2) is arranged on the plurality of jacks (18).

4. The experimental device for debonded lining with low-frequency excitation and high-frequency impact coupling according to claim 3, characterized in that, The loading mechanism includes: A plurality of servo electric cylinders (3) are arranged circumferentially of the lining ring (2). The outer ends of the servo electric cylinders (3) are fixed to the main frame (1). A rigid plate body (4) is fixed to the inner ends of the servo electric cylinders (3). A nylon gasket (5) that presses against the outer wall of the lining ring (2) is arranged on the inner side surface of the rigid plate body (4). The inner side surface of the nylon gasket (5) has a conforming surface adapted to the outer wall of the lining ring (2).

5. The test device for debonded lining with low-frequency excitation and high-frequency impact coupling according to claim 1 or 2, characterized in that The vibrator (7) is suspended at the lower end of the support beam (6) through an elastic member. The vibrator (7) is located inside the lining ring (2) and within the longitudinal projection area of the lining ring (2).

6. The test device for the debonded lining with low-frequency excitation and high-frequency impact coupling according to claim 1 or 2, characterized in that Slide bars (13) are longitudinally arranged on both sides of the top frame (9). Slide sleeves (14) are respectively arranged on both sides of the truss (10). The slide sleeves (14) are in sliding cooperation with the slide bars (13) on the same side. The electric unhooking device (11) is used to drive the truss (10) to lift and lower.

7. A test method for a debonded lining coupling low-frequency excitation and high-frequency impact, which uses the test device for a debonded lining coupling low-frequency excitation and high-frequency impact as described in any one of claims 1-6, is characterized in that Including the following steps: S1. Fabricate a steel mold in proportion, pour the lining ring (2) using the steel mold and install it inside the main frame (1). S2. Install a loading mechanism inside the main frame body (1). The loading mechanism circumferentially compresses the lining ring (2) to simulate the surrounding rock load in the circumferential direction of the lining. S3. Install a vibrator (7) on the support beam (6). The support beam (6) axially penetrates the lining ring (2) and positions the vibrator (7) inside the lining ring (2). Electrically connect the vibrator (7) to a power amplifier (8). S4: Install the truss (10) on the electric unhooking device (11) at the top of the top frame body (9), and install a drop hammer (12) at the bottom of the truss (10). S5: Turn on the vibrator (7) to simulate the low-frequency excitation of a train passing through the lining, and disconnect the electric unhooking device (11) to enable the drop hammer (12) to inertially disengage from the truss (10) and impact the lining ring (2) to simulate the high-frequency impact of a falling rock on the lining. S6: Obtain single-factor data of low-frequency excitation or high-frequency impact, or obtain coupled data of low-frequency excitation and high-frequency impact.

8. The test method for the debonded lining with low-frequency excitation and high-frequency impact coupling according to claim 7, characterized in that, In step S1, a 1:10 steel mold is made through on-site measurement or actual drawings. According to the reduced-scale model test, the elastic modulus is taken as 1 / 10 of the prototype concrete. After pouring the lining ring (2), it is cured indoors for 28 days to reach the standard compressive strength, and then the steel mold is removed.

9. The test method for the debonded lining with low-frequency excitation and high-frequency impact coupling as claimed in claim 7, characterized in that In step S3, the power amplifier (8) is connected to a digital signal source, and the digital signal source is connected to a computer control device. The output mode is two-channel synchronous output.

10. The test method for the debonded lining with low-frequency excitation and high-frequency impact coupling according to claim 7, characterized in that, In step S4, the electric unhooking device (11) controls the lifting and lowering adjustment of the truss (10) inside the top frame body (9), and different masses of drop hammers (12) are replaced to simulate the erosion of the lining ring (2) by different magnitudes of impact forces.

Images